Various embodiments described herein relate to light emitting devices and assemblies and methods of fabricating the same, and more particularly, to Light Emitting Diodes (LEDs), assemblies thereof and fabrication methods therefor.
LEDs are widely known solid-state lighting elements that are capable of generating light upon application of voltage thereto. LEDs generally include a diode region having first and second opposing faces, and include therein an n-type layer, a p-type layer and a p-n junction. An anode contact ohmically contacts the p-type layer and a cathode contact ohmically contacts the n-type layer. The diode region may be epitaxially formed on a substrate, such as a sapphire, silicon, silicon carbide, gallium arsenide, gallium nitride, etc., growth substrate, but the completed device may not include a substrate. The diode region may be fabricated, for example, from silicon carbide, gallium nitride, gallium phosphide, aluminum nitride and/or gallium arsenide-based materials and/or from organic semiconductor-based materials. Finally, the light radiated by the LED may be in the visible or ultraviolet (UV) regions, and the LED may incorporate wavelength conversion material such as phosphor.
An LED component provides a packaged LED die for mounting on a board, such as a Metal Core Printed Circuit Board (MCPCB), flexible circuit board and/or other printed circuit board, along with other electronic components, for example using Surface Mount Technology (SMT). An LED component generally includes an LED die and other packaging elements.
SMT is a method for producing electronic circuits in which the components are mounted or placed directly onto the surface of circuit boards. An electronic device so made may be called a Surface Mount Device (SMD). An SMT component is usually smaller than its through-hole counterpart. Simpler and faster automated assembly may also be provided, as well as other potential advantages. As such, SMT is increasingly being used in electronic component assembly.
SMDs often use lead frames as part of the SMD package. A lead frame is a metal structure inside a package that carries signals from the die to the outside. The die inside the package is typically glued to the lead frame and bond wires attach the die contacts to the lead frame leads using wire bonding techniques. The lead frame may then be molded in a plastic case, and the outside of the lead frame is cut off, thereby separating the leads. The lead frame itself may be manufactured by removing material from a flat plate of copper or copper-alloy, by etching, stamping and/or other techniques.
Lead frames are also now being used for low cost, high density SMD LED components. In these LED components, the lead frame includes a metal anode pad, a metal cathode pad and a plastic cup on the metal anode pad and the metal cathode pad that defines an exposed portion of the metal anode pad and an exposed portion of the metal cathode pad in the plastic cup. At least some portions of the plastic cup may be transparent, translucent, opaque and/or reflective, and the plastic cup may be formed of plastics, such as Epoxy Molding Compounds (EMCs) and/or silicone. An LED die is glued to the lead frame, and the anode and/or cathode contacts thereof are wire-bonded to the lead frame pads. The cup may then be filled with encapsulant, at least some portions of which may be transparent, translucent and/or reflective. The encapsulant may include wavelength conversion material, such as phosphor, therein.
LEDs are increasingly being used in lighting/illumination applications, with a goal being to provide a replacement for the ubiquitous incandescent light bulb. The cost of manufacturing LED dies may continue to decrease due to advances in microelectronic fabrication techniques. As such, the packaging the LED dies may assume a larger and larger cost of the LED component.